DESCRIPTION (Adapted from Applicant's Description): Osteoporosis is a geriatric disease that has pediatric origins. Development of peak bone mass, which is achieved by the third decade of life, is influenced by behaviors during childhood and adolescence, most notably calcium consumption and physical activity. During the pubertal years, 45% of the adult skeletal mass and 15% of adult height are gained. National and local surveys indicate that adolescent girls have inadequate calcium intakes and lower than recommended levels of physical activity. Although school-based programs have shown promise in affecting risk factors for cardiovascular health, application of behaviorally-based programs to target bone health have been limited. The primary goal of this proposal is to develop and evaluate a school-based nutrition and physical activity program, called BONES (Beat Osteoporosis Now by Exercising and Eating Smart), to enhance future bone health in girls. Elements of the BONES program will be based on Social Cognitive Theory (SCT) and will include both behavioral (student-oriented classroom lessons) and environmental (school food service, physical education) components. The program will consist of two phases: a feasibility trial in which intervention materials and measures will be pre-tested and validated, and the main intervention trial. Eighteen ethnically diverse middle schools from central Texas will be randomized into control or intervention conditions, with schools serving as the unit of randomization and analysis. Nine of the schools will receive the 2-year intervention (BONES), while the control schools will continue their usual health programs. It is hypothesized that students in intervention schools will, on average, (1) have a 3% greater calcaneus ultrasound Stiffness Index, (2) consume 2 more servings/day of calcium- containing foods, and (3) engage in 17 more minutes/day of vigorous physical activity compared to students in the control schools. Secondary hypotheses at the student level are: intervention students will (1) demonstrate higher scores in self-efficacy, knowledge of bone health, calcium-containing foods and exercise; and (2) have higher mean intakes of calcium and average greater frequencies of weight bearing type exercises per day compared to students in the control schools. Secondary hypotheses at the school level are: intervention schools will offer (1) more calcium-containing foods; and (2) more opportunities for weight-bearing activities than control schools.